The 25-year-old Nottinghamshire opener made 101 off 105 balls, with 13 fours, as the Lions ran up 339 for five after winning the toss. Ravi Bopara (74), Jason Roy (51) and Jonny Bairstow (50 not out) were the other main contributors.

In reply Sri Lanka A were bowled out for 288 after being 160 for two in the 30th over. Dinesh Chandimal top-scored with 73, while Ravi Patel took three wickets for 71 runs from 10 overs and there were two wickets each for Harry Gurney, Boyd Rankin and Bopara.

At the start of the day Hales and James Vince took the total to 33 before Vince pulled Lahiru Gamage to long leg and was caught by Lahiru Jayaratne for 10.

Hales grew in confidence and, helped by Bopara, saw the Lions to 57 after 10 overs. The opener went to his 50 in the 18th over when he took two to midwicket off Chathuranga De Silva, having 50 balls with eight fours.

Bopara reached his half-century in the 30th over when he hit Ramuth Rambukwella to the deep extra cover boundary, his runs coming off 74 balls with two fours.

Hales moved into the 90s with consecutive fours and went to his century off the first ball of the 37th over when he hit Gamage back over his head for a first bounce boundary. By then he had faced 104 balls and struck 13 fours.

Next delivery Gamage bowled a leg side full-toss which Hales lifted to fine leg, where Danushka Gunathilaka took the catch. The second wicket partnership had added 165 runs in 30.1 overs.

One run later Bopara, on 74, clipped Gamage to Seekkuge Prasanna at midwicket. That brought in Roy, who soon made his intentions clear by hitting the first six of the innings.

Roy took four consecutive sixes over long on to the dismay of bowler Sachith Pathirana. After a dot ball he hit another six off the last delivery, - bringing up his half-century off 22 balls with two fours and six sixes.

Without addition Roy was bowled by Jayaratne, at which point the the Lions were 255 for four in the 43rd over.

James Taylor and Bairstow went on the offensive and took 24 off the 47th over bowled by Jayaratne. De Silva returned to bowl the 49th over and second ball had Taylor caught off a top edge at short fine leg by Gamage for 31.

Bairstow went to his half-century off the penultimate ball of the innings to end unbeaten, having faced 30 balls and hit five fours and two sixes.

When Sri Lanka replied Gurney made an early breakthrough when Mahela Udawatte was caught by Hales at first slip after the chance was juggled by Smith at second.

Gunathilaka was caught by Craig Overton at long on for 57, then Chandimal went for 73, including five fours and three sixes, when he was bowled by Bopara.

Bhanuka Rajapaksha made a brisk 33 before he was caught at midwicket, while Prasanna was caught at deep backward point by sub David Willey off Rankin.

Gurney then returned at the Old Pavilion and with his second ball dismissed De Silva, caught by Bairstow for four.

Bopara came back on and first ball had Pathirana well caught low down by Hales, running in from the Atkinson Pavilion.

Overton then bowled Ashan Priyanjan for 33 off a bottom edge which left Sri Lanka needing 100 off eight overs with two wickets remaining. The Somerset player had a hand in the next wicket when he caught Gamage at midwicket off Rankin.

Rambukwella hit some late blows before he was bowled by Patel for 22 - and Sri Lanka A were all out for 288 in 49 overs.

After the game, Hales said: "It was a good wicket to bat on, with pace early on, but in the middle it was pretty hard work against the spinners.

"Me and Ravi knew that if we set a platform we could give the guys like Jason and Jonny license later on. We did that and it was a pretty well constructed innings all round.

"If you look at the talent there is in the Lions squad, every single one of the guys will have an eye on the winter squads for the senior team.

"The challenge for everyone is to perform at that level and I think this is a really good changing room to be in.

"I am really hungry for an England one-day spot and it was one of my aims at the start of the season, particularly after my poor year in red ball cricket last year.

"I wanted to perform well in the Championship for Notts and I have done that. Now my next challenge is to put pressure on to get into that senior England 50-over side. I feel in good form at the moment for these next three fixtures."